Draw the structure of the following complexes. What are the oxidation state, coordination number, and coordination geometry of the metal in each?
(b) [Cr(NH3)2(C2O4)2]NO2

Verified step by step guidance

1. Determine the oxidation state of Cr: Assume the oxidation state of Cr is x. Ammonia (NH3) is a neutral ligand, and oxalate (C2O4) is a bidentate ligand with a charge of -2. The complex is overall neutral, so x + 2(0) + 2(-2) = 0. Solve for x.
2. Identify the coordination number: Count the number of ligand donor atoms attached to the metal. Each NH3 contributes 1 donor atom, and each C2O4 contributes 2 donor atoms. Calculate the total.
3. Determine the coordination geometry: Based on the coordination number, predict the geometry. Common geometries include octahedral, tetrahedral, and square planar.
4. Draw the structure: Arrange the ligands around the metal center according to the determined geometry. Indicate the bidentate nature of the oxalate ligands.
5. Consider the counterion: Note that NO2 is the counterion and does not affect the coordination sphere of the complex.

Key Concepts

Oxidation State

The oxidation state of an element in a compound indicates the degree of oxidation of that element, reflecting the number of electrons lost or gained. In coordination complexes, the oxidation state of the metal can be determined by considering the charges of the ligands and the overall charge of the complex. For example, in [Cr(NH3)2(C2O4)2]NO2, the oxidation state of chromium can be calculated based on the charges contributed by the ammonia and oxalate ligands.

Coordination Number

The coordination number refers to the total number of ligand atoms that are directly bonded to the central metal atom in a coordination complex. It is determined by the number of donor atoms from the ligands that coordinate to the metal. In the case of [Cr(NH3)2(C2O4)2], the coordination number can be assessed by counting the donor atoms from the two NH3 ligands and the two oxalate ligands.

Coordination Geometry

Coordination geometry describes the spatial arrangement of the ligands around the central metal atom in a coordination complex. Common geometries include octahedral, tetrahedral, and square planar, which depend on the coordination number and the steric and electronic properties of the ligands. For [Cr(NH3)2(C2O4)2], the coordination geometry can be inferred from the coordination number and the nature of the ligands involved.